1.8T Engine - Need Help Diagnosing Coolant Leak

[A4orce84]

Hello Everyone,

I've been having a coolant leak over the past month and have been trying to identify where it is coming from on my 2004 B6 A4 1.8T. It started about a month ago after I'd come home and leave (few hours later) I'd find a small coolant puddle on my garage floor:
https://imgur.com/a/SK7gv

Background:
I took the car to the independent mechanic here in town and he also is having trouble tracing where the leak is coming from. He put 20 or so PSI on the coolant system, and let it go for 10-15 mins to see if he could spot where the leak was coming from. Unfortunately, he said he was unable to trace the leak. He checked the usual spots (thermostat, oil cooler, water pump, Jplug, etc.) and the ONLY thing he mentioned was he saw some pink crustiness on the bottom of the coolant flange. There is no dried coolant 'vomit' on the back of the engine, where a usual coolant flange leaks, so again I'm not sure how accurate that the flange is leaking to be honest. Also, a lot of those components have been replaced in the last year and should not be leaking (specifically: Thermostat, J-Plug, CTS, Radiator).

Possible Cause:
Since it seems to only leak when things are 'cooling down', I'm not sure if that means it's an o-ring or plastic piece that is possibly shrinking as things cool down. When the car is on and the coolant system is under load, the o-ring is working as expected, and it starts leaking when things are cooling down and the car is off. That is the only thing I can come up with that would make sense, but the question still is where is it coming from. But, hey I could be completely wrong and it is something else that is the root-cause of this coolant leak as well.

Any ideas on possible weak points on where my coolant leak is coming from would be greatly appreciated. If anyone needs any additional information to help in the troubleshooting process, please let me know!

Thanks,
Asif

[IceQB]

Should try checking all coolant pipes for possible tears.
I also had a leak I couldn't locate, drained coolant & replaced with "approved" coolant.
Leak dissapeared.

[egovreau]

If the coolant flange hasn't been replaced, you might want to anyway. Specifically, go with the aluminum one that URO Tuning sells. It's a bit pricey, but worth the knowledge that is a piece of plastic that won't fail.

And you did say there's a pink crust forming there.

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[A4orce84]

Well that's what the indy mechanic said. And while he might be right, @Matt Devo helped me poke around the engine last night and we did not see any pink crustiness on the bottom of the flange as far as we could tell. I've gone down the rabbit hole of replacing parts and it not being the actual root-cause issue, and I would rather save the money on a metal flange (when mine is working as far as I know) and use it toward the actual part that is failing.

I may go get a 2nd opinion from another mechanic and see what they say, but to say the least this does not sound like an obvious coolant leak unfortunately.

Thanks for the feedback and suggestions!

[A4orce84]

Bump, TTT.

[Timtheguru]

Nice pic.. lol

Probably your water pump. Same thing happened to mine, PO had timing belt changed and in <6k miles it would leak once the engine cooled down. Ended up that they didn't clean the sealing surface for the water pump where the o-ring sits.

Cycle of events that cause a leak:

Start car > engine warms up and metals expand creating a seal > engine re-fills with coolant from expansion tank > turn off car > engine cools down and metals shrink > engine leaks coolant where the metals shrunk > engine is "low" on coolant in the block > repeat...

Here's a pic from when I fixed my leak. You can see the trail coming from the water pump. There wasn't any crusty stuff in there, just wet. It would only leak on cooldown.

[rocket1420]

It's possible your coolant tank is peeing. If you take the cap off you can see the overflow port. Does your cap click when you tighten it down?

[A4orce84]

Hello Everyone,

I am still struggling with this leak so wanted to bump this thread up. So, let me answer a few things.

It's possible your coolant tank is peeing. If you take the cap off you can see the overflow port. Does your cap click when you tighten it down?
It clicks down properly when I tighten it and no coolant is 'peeing' as far as I can tell.

Wanted to see if anyone else had any suggestions on where my coolant leak might be coming from? Thanks in advance!


Thanks,
Asif

[Timtheguru]

Did you rule out the water pump location? You will need a mirror and a flashlight, but you can get the top cover off and have a look inside.

[A4orce84]

Did you rule out the water pump location? You will need a mirror and a flashlight, but you can get the top cover off and have a look inside.

Will be confirming this very soon.

[doc_oc]

Can you at least narrow it down to one side of the engine? Front, back, driver, passenger?
2 things to try, and pretty cheap too, find a car wash with a warm water pressure washer and go to town on the engine bay. Maybe remove the plastic belly pan. Then inspect and see where it's coming from.
Go and get a coolant dye and light. 20-30$ and it's pretty easy to find the root cause.

You can't get much help here without giving us at least one of the 4 sides of the engine. There is coolant going through the turbo too. There is lots of hoses, pipes and flanges that can crack/break.
Heater core and connections to it can be another culprit.

Good luck.


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[A4orce84]

Hello Everyone,

Sorry for the delay. I have a few updates to this issue recently:
---------------------------------------------------------------------------------------------------------

Did you rule out the water pump location? You will need a mirror and a flashlight, but you can get the top cover off and have a look inside.

Confirmed. Replaced with a new HEPU water pump and issue still persists.

Can you at least narrow it down to one side of the engine? Front, back, driver, passenger?

Coolant leak appears to be from front / front driver-side area. Picture below of my garage so you get an idea:
https://imgur.com/a/zaqKc
---------------------------------------------------------------------------------------------------------

Copying from my original post....the following items have been replaced or checked and are not leaking currently:

0. Waterpump (replaced)
1. Thermostat (replaced)
2. J-Plug (replaced)
3. CTS (replaced)
4. Radiator (replaced)
5. Coolant Flange (not leaking)
6. Oil Cooler (not leaking)

At this point, starting to run out of ideas on where the 'cool-down' leak is coming from. Any assistance, ideas, feedback, etc. would be greatly appreciated.


Thanks,
Asif

[doc_oc]

Go get a coolant dye and uv flashlight from an auto car parts store. The easiest way to find out where it's coming from.

There are a few hoses and pipes on that side of the engine. Both inlet and outlet hoses to the radiator. On the lower hose there is a temp sensor and a plug as well.
So, if you can't find the leak just by looking around....use the dye.


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[caluma4x4]

So, the Indy saw some pink crustiness below the coolant flange but it’s not leaking? Well it must be the only one on the planet that isn’t. Funny to see that you’ve replaced the far more expensive items first. I’d just replace the coolant flange now, the centre part that the o ring seats against erodes and that’s why it leaks.

https://www.google.co.uk/search?q=pa...tkT7PrY_EZ6qM:

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[BARRY]

i wouldn't doubt it...clean off the area...check back in a week. if more crust then you have your problem right there.

[shinrai]

I just went through this same scenario - leak would persist only when engine cooled down. Same area as yours as well. Was a bugger to find because it’s difficult to see around T-stat area. Turned out to be lower rad hose where it connects into the T-stat housing. I’m not sure if it was the actual o-ring or elbow but changing the complete hose fixed the leak. Get an OEM hose. Also get a new o-ring for the sensor.

[BARRY]

that's some good advice right there.

[A4orce84]

Hello Everyone,

Just wanted to provide a quick-update on this issue. I am still battling this coolant leak unfortunately, trying to identify where exactly it is coming from.

Update:
I ended up purchasing some dye and tossing it in the coolant tank to trace my leak better. I pulled off the belly pan and got the car on ramps, ran it up to operating temperature, and then shut the car down. Came back after 30 mins to find the following:

Pictures (Please make sure you are using the photobucket extension):







------------------------
Any ideas where the leak is coming from based on the pictures above? It appears to be coming from ABOVE the oil pan, in that small gap/hole area near the top. However, looking at the top of the engine, I cannot see anything really lighting up. All normal areas (coolant flange, J-plug, etc.) look fine and are not showing any neon-green coolant. It seems to be dripping down from somewhere above the oil pan, on the driver's side.

Any ideas, assistance, feedback, etc. would be greatly appreciated. Thanks in advance!

[doc_oc]

Thermostat housing? Radiator hose to the thermostat housing? There is a hard metal pipe as well there. If memory serves me right, it's the turbo coolant line.
You have to keep digging in that area. Use a mirror and the uv lamp. You will find it.
Check the head gasket area as well.

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[Ol Dirty Noodle]

Looks like something metal is cracked right above the bolt with the coolant on it

[BARRY]

i couldn't figure out my coolant leak so i brought my car to a specialist. they pressurized the system and found a steady flow coming from my turbo coolant feed line. the rubber line specifically as there was a split in the line. replacement was $11. this was impossible for me to diagnose as it didn't always leak.

[A4orce84]

i couldn't figure out my coolant leak so i brought my car to a specialist. they pressurized the system and found a steady flow coming from my turbo coolant feed line. the rubber line specifically as there was a split in the line. replacement was $11. this was impossible for me to diagnose as it didn't always leak.

Thanks Barry, if you read the original post I actually took it to the local mechanic here in town. They did a pressure test as well and they were unable to determine the cause of the leak. This is due mainly because the leak would occur only after everything cooled-down, and did NOT leak while the engine was warm.

[A4orce84]

So I also had a coolant issue.

I just bought a garaged B6 A4 with 65,000 miles on it. Mint condition.
I've driven it for about 10k miles and the ESP and Traction control light came on. Some research I ended up replacing the Crankshaft sensor. Turned it back on, the problem persists with a check engine light now on. Fast track, dropped off at dealership. They said the thermostat sensor malfunctioned and dumped coolant into my wire harness (complete repair $2000USD) they said this could be only the
initial problem as the ECM could be malfunctioning (another 1000USD). And the rabbit hole continues...
Thoughts, should I give them the go ahead? How is this preventable from happening again? Any advice welcome.

Hey kin3tiks,

As I still have an issue with my car (and as the OP), I'd kindly request you not to hijack my thread full of posts around my issue currently. If you could start a new thread and get feedback and replies there, that is probably the best course of action. That way you also have all the focus on your specific issue and not 'muddy the waters' with my issue and feedback and troubleshooting thus far.

Thanks!

[kin3tiks]

Hey kin3tiks,

As I still have an issue with my car (and as the OP), I'd kindly request you not to hijack my thread full of posts around my issue currently. If you could start a new thread and get feedback and replies there, that is probably the best course of action. That way you also have all the focus on your specific issue and not 'muddy the waters' with my issue and feedback and troubleshooting thus far.

Thanks!

Sure thing!

[jjvwg]

Your mechanic should have left your cooling system pressurized for a few hours in order to let it test from the time it was warm, through cool down, and when cold to get it to actually leak. At this point, having done the dye it should point you in the right direction. Looking the the pic of the oil pan with the sensor shown, and the location of the drip it sure looks like the water pump to me.

[A4orce84]

Your mechanic should have left your cooling system pressurized for a few hours in order to let it test from the time it was warm, through cool down, and when cold to get it to actually leak. At this point, having done the dye it should point you in the right direction. Looking the the pic of the oil pan with the sensor shown, and the location of the drip it sure looks like the water pump to me.

Thanks for the input. The water pump was recently changed (December 2017), along with the following components recently:

0. Waterpump (replaced)
1. Thermostat (replaced)
2. J-Plug (replaced)
3. CTS (replaced)
4. Radiator (replaced)
5. Coolant Flange (not leaking)
6. Oil Cooler (not leaking)

Please let me know if you have any other questions or feedback. Thanks!

[old guy]

Just because the components were replaced doesn't preclude them from leaking. Looking at where your coolant is leaking it could be the thermostat housing, the lower hard pipe connection to the thermostat housing, the coolant drop line from the upper hard pipe to the thermostat housing or the J plug. I suspect it is one of those components.

[BARRY]

in the past i've had leaks through heater lines upon cool down. guess the o-rings shrunk over time. replaced the entire line and all was well afterwards. usually didn't happen right away or all the time. i did catch a drip hanging one day, and that's how i caught it.

[jjvwg]

Just because the components were replaced doesn't preclude them from leaking.

THIS. and now that i re-look at you pictures on a computer i realized i was looking at the one picture wrong and am seeing that its the drivers side of the motor now. I agree with old guy as far as components that could be leaking are concerned. might be easiest to pull your intake manifold off to get a better look at things.

[imnuts]

A pressure test kit at Harbor Freight is rather cheap. You could pick one up, pressurize the system, and start looking for damp spots or drips. The kit also comes with several adapters so you can use it on more than just the A4 should you get/have different vehicles.

Sent from my Pixel 2 XL

[ozMatt]

not to flog a dead horse, but Old Guy is right, and shinrai touched on it in post #16 as well. In your pics with the dye, that bolt is practically right under where the thermostat is positioned on the block.

The only parts in that space exposed to coolant are the thermostat, j-plug, and the three hoses that attach to the thermostat. When you next have time to look at it, try removing the throttle body (and hose) to see if you can get a better look in that area. It may also give you enough room to get your hands in there to feel for any leaks you can't see.

Good luck.

[customa4]

When you changed your thermostat, did you replace the o-ring on the coolant hard pipe going into the thermostat? I had a similar issue where I couldn't find the leak and when I inspected that o-ring it was completely flat and not sealing. My guess is it's leaking at that o-ring.

[shinrai]

Just because the components were replaced doesn't preclude them from leaking.

Absolutely. If you do take it apart again be sure to clean up the sealing area on the block where the thermostat housing attaches to the block. You'll need a Dremel tool with a wire brush attachment or something similar.
Your leak pics looked exactly like mine. Go with OEM equipment or you'll likely have to do this again in the near future.

[A4orce84]

Absolutely. If you do take it apart again be sure to clean up the sealing area on the block where the thermostat housing attaches to the block. You'll need a Dremel tool with a wire brush attachment or something similar.
Your leak pics looked exactly like mine. Go with OEM equipment or you'll likely have to do this again in the near future.

Based on everyone's feedback I am going to order the following parts from ECS to start:


Will keep everyone posted on how it goes. Thanks again everyone for your help with troubleshooting this issue! It is greatly appreciated! =)




Thanks,
Asif

[customa4]

You're wasting your money ordering a thermostat. O-rings will be the only things actually causing the leak. That thermostat is also overpriced. I think Behr is the OEM manufacturer for our cars if I remember correctly.

Edit: Here's the OEM thermostat which is also cheaper. Click I still don't think you need it though.

[A4orce84]

You're wasting your money ordering a thermostat. O-rings will be the only things actually causing the leak. That thermostat is also overpriced. I think Behr is the OEM manufacturer for our thermostats if I remember correctly.

I took this into consideration. The thermostat I currently have on the car is a cheapo HT thermostat (could be the root-cause of the problem, could be something else). However, I figured just having a new thermostat on hand in case is better than tearing everything down / putting it back together, only to find out I will need to do the whole job over again in a few weeks due to it being an issue with the thermostat. Best case scenario, I return the thermostat to ECS and only have to replace the o-rings as you suggested.

ECS has a better return policy than Europa (Full refund vs. partial), so that's why I ordered everything from ECS together.

"An ounce of prevention is better than a pound of cure..."

Thanks for looking out though, appreciate it!

--------------------
Edit: Around "OEM" thermostat and brands, Behr was the OEM manufacturer but has since become Behr/Mahle due to a merger a few years ago:
https://www.mahle.com/en/news-and-pr...re-in-behr-399

That being said, I'm pretty sure the Mahle version is the same as the Genuine OEM "Audi/VW" version, just without the Audi/VW branding on the part itself.

[BARRY]

werd...i installed a cheapo thermostat on my sedan and it worked great.....for 2 years. in saying that everybody on the forums is correct that OEM is the best way to go.

[Wet0willy01]

I replaced a rear coolant flange on my girlfriends b6 because of a coolant leak. I could tell someone else had struggled with it before by the amount of rtv on the o-ring/flange, and a spare o-ring laying in the battery tray. Then it was leaking from the heater hose connection. So I ordered a new aftermarket heater hose (after 3 different o-rings in the hose end failed to seal). It still continued to leak with a brand new hose and newly replaced rear flange. I got an used OEM hose from a member on here and another aftermarket coolant flange and it finally stopped leaking. So even though the parts were new, they still leaked.

[customa4]

I did the same. Mine was leaking from the bottom hose/connection of the coolant flange at one point too. I also used an aftermarket hose and it came back to bite me. OEM or bust just about 99.9% of the time. You might save $30 on the hose but you’ll end up paying twice as much when you have to purchase the OEM piece shortly after to actually fix the problem.

[kjmiles]

Was there any resolution to this? My car is doing exactly the same thing. I just had the coolant flange, j-plug and thermostat replaced as well as a few hoses (not sure which ones). I've had it to my mechanic 4 times in the last 6 weeks and now it's leaking again. One drip I see on the floor near the front (maybe lower hose), but more on the floor where the back of the engine would be. You're not alone! Anxious to see what you found. I'm like $1300 into this problem.
KJ